Trees contribute to our environment and well-being in a wide variety of ways, as demonstrated in this video from the Nature Conservancy.
The Trees Are Good website of the International Society of Arboriculture describes the many benefits that trees offer, including societal, communal, environmental, and economic. The article What is a tree worth? shows how scientists are discovering the crucial role that trees play in the green infrastructure of American cities.
The role of trees in home energy conservation is well illustrated by this video from This Old House.